One way to picture well-to-do: a household where the bills are already covered before anyone asks. Not new money, not showing off — a family that has been doing well for long enough that money has stopped being a question. The phrase itself can be read as doing well, tied into one word: to do here is about how life is going, not about a job to finish.
well-to-do 可以想成一個帳單早就付好的家。不是剛發財，也不是拿出來炫耀，而是日子好了夠久，錢已經不成為問題。這個詞本身可以讀成 doing well（過得好）被綁成一個字——裡面的 to do 講的不是「做某件事」，而是「過得怎麼樣」。它的兩個用法，差別只在這份「過得好」是掛在某個家庭身上，還是拿來圈出一整群人。